1st Nordic Drying Conference - NDC'01, Trondheim, Norway, June 27-29, 2001

DRYING KINETICS IN A CONCURRENT SPRAY DRYING TOWER Ireneusz Zbicinski1, Agnieszka Delag, Czeslaw Strumillo Technical University of Lodz, Faculty of Process and Environmental Engineering, 213/215 Wolczanska St., 93-005 Lodz, Poland, 1phone (+48+42) 631 37 91, fax. 636 49 23 zbicinsk@ck-sg.p.lodz.pl, delag@ck-sg.p.lodz.pl Key words: PDA analysis, microseparator measurements, residence time ABSTRACT A method for measuring drying kinetics of different products in a disperse system has been developed in the Faculty of Process and Environmental Engineering, Lodz Technical University. In order to analyse the mechanism of spray drying process a nine meter long concurrent spray drying tunnel was designed, built and tested. The tower was equipped with optical glass windows to perform measurements using laser technique (LDA, PDA) and to measure the temperature of the drying agent by a microseparator. The windows also enable taking samples of material being dried. Baker's yeast was used as a raw material in the experiments. Extensive spray drying tests were performed to determine the influence of operating process parameters on spray drying kinetics. To determine spray drying kinetics three groups of experiments were made: measurements of moisture content by sampling and laboratory analysis of water content, measurements of drying agent and sprayed material temperature inside the spray envelope using a microseparator, PDA analysis of local and average particle size distributions for different distances from the atomizer and distribution of axial velocity of different droplets fraction. Results enabled us to find a relation between time and length scale in the tunnel and as a consequence to present and discuss examples of spray drying kinetics showing changes of moisture content of a product versus time (first in the literature). Average residence time of the spray as well as residence time of particular fractions were also determined.

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